Pulmonary artery flow changes with inspiration which draws both air and blood into the chest. Expiration reduces venous return to the right side of the heart. This is a basic physiologic variable, but is difficult to measure, as both invasive catheter techniques and ultrasound have limitations. We used respiratory and cardiac gated cine-PC - a technique developed at the Lucas Center to quantify the degree of phasicity of pulmonary flow with inspiration. We also evaluated whether non-respiratory gated cinePC (which is a much faster method) is accurate in comparison with respiratory gated cine-PC. Methods and Results Nine healthy volunteers were scanned on the 1.5 T syatem at the Lucas Center. All subjects had respiratory resolved cine-PC, producing 16 cardiac time frames for each of 8 respiratory frames. Subjects also had non-respiratory gated cine-PC. Main pulmonary artery (MPA) flow was integrated over hand drawn regions of interest on a SUN workstation. Peak inspiratory MPA stroke volume averaged 99.1 mi; peak expiratory flow averaged 72.8 ml. Mean respiratory phasicity (peak inspirati9n - peak expiration I peak inspiration) was 25+8%. Mean nonrespiratory resolved flow was 96% and 112% of inspiratory and expiratory flow. The degree of respiratory phasicity correlated inversely with heart rate. Discussion (1) MPA respiratory phasicity averaged 25% in supine volunteers, slower heart rates were associated with greater respiratory phasicity. Right heart constrictive disease may alter phasicity. (2) Conventional respiratory compensated (not gated) cine-PC measures minimally lower flow, probably because the center of k-space uses expiratory frames. For bulk MPA flow measurements however, nonrespiratory gated flow measurements are sufficiently accurate.